Stuck in 4 lo help

The ADD does not cycle in 4Lo. The only change between 4Hi and 4Lo is in the T case.

 

Yes. There is no pavement right now. It’s all loose snow.

I read through most of those threads (thank you for those!). Those for sure helped me understand how the ADD was working.

 

Thank you for that. That would explain why I can’t hear it move.

So after that fork moves to 4hi in the ADD, what happens in the transfer case to change it into 4lo?

 

Another similar mechanism in the tcase goes from 2Hi <> 4Hi <> 4Lo.

Also I'm a bit confused why everyone is saying keep your foot on the brake or apply parking brake etc. In all my experience it helps a lot to be rolling (slowly) when making the Hi / Lo switch.

I'm curious what exactly happened when your wife did the initial switch? Flipped it to 4Lo and instantly flipped it back to 4Hi? Was it in gear? Trying to figure out exactly how we got here

 

You're welcome!

For 4Hi, the T case actuator presses against the synchro to spin up the front drive shaft and engage high range dog. ADD connects the axle shaft.

For 4Lo, the T case actuator just throws further to move the dog from the 1:1 high range gear set to the 2.57:1 low range gear set. There is no synchro, so it has to be done at a stop.

 

The 3rd Gen has a somewhat different 4WD system. Some of the tricks and functions are different. Overall, there are no gray wire mods for the 3rd Gen. Kinda sucks.

More to your question though, see below. I know on the MT side, the T case actuator will not move until it senses the limit switch on the clutch. It'll literally just wait for it. My guess is that for the AT, it uses the brake light switch for the same thing?

 

Thank you! Just found a good thread to read and learn about how that all works.

The truck was parked in our driveway in 4hi . It’s steep and snowy so the truck is usually in 4wd.

She said she flipped the switch to 4lo by mistake in park and then shifted into drive. When she got back she said the truck was stuck in 4lo.

 

that must have taken a while. must have been loud with that screamin' straight cut low gear. if you don't hear a click it the actuator might be frozen or it may have gone into some sort of fail-safe mode.

 

I think you can get to 4Lo from Park. I haven't played there to know. The couple times that I saw ATs going to 4Lo was in Neutral.


Earlier, you thought it might be the switch. It is pretty robust for what it is and is pretty easy to disassemble if you really want to have a look. @MESO has a video for the chrome trim swap. Just keep any eye out for the black plastic nubs that some folk have lost. IMHO, if it is still stuck in 4Lo at this point, it may be deeper than that and you would need help from others folks if you are going to dig out the multimeter and start probing around. See some posts by @BigWhiteTRD . He helped some folks with 4WD issues.

The switch disassembly is in this vid:

​

 

I found this video from another thread.

I think this is exactly the same issue I’m having. I will try and pull that apart tomorrow and worst case get out of 4lo.

 

Have you tried to fully disengage 4wd and put it into 2wd? If it is in 4Lo, make sure the switch is also in 4Lo before starting the truck. Start the truck and shift to neutral, now turn the switch to 4Hi. Wait for a minute and if needed let off the brake and let the truck roll slowly come back to a complete stop and see if anything changes. Regardless of what happens I would now shift into 2wd and see if 4wd disengages.

 

Yup, tried all of that

 

Have a copy of techstream? Able to see if there are any abs system faults that are keeping it from working? Abs system faults can keep the 4wd system from engaging or disengaging.

 

I don’t have tech stream unfortunately. I did run a scan with Carista bough and no codes came up.

 

I highly highly suggest testing everything electrically to learn the actual state of the t-case and ADD actuators before taking anything apart. I personally worked on a buddies 3rd gen that was having similar issues and he showed me a few videos like that. It works great to get back to 2Hi, but we were never able to successfully retime the t-case actuator 100%. Tried several times. As I said, it was enough to get back into 2Hi and make the truck happy, and I think we could even shift into 4Hi a few times. But we were never able to get into 4Lo without it getting stuck again. The truck would shift into 4Lo, but it would never shift out. Youll notice that video you posted does not show him shifting back, he just keeps it in 2Hi and calls it good.

Let me look around for schematics, think I still have those somewhere. The overall operation and components of 3rd gen is similar to the 2nd gen trucks. Should be able to back probe a few connectors and tell what limit switches and detection switches are made and which are not - so we know what state the system is actually in. I would even say you could even unplug the t-case actuator and power the motor with a 9v battery to get back to 2Hi before you open it up.

3rd gens do have a few DTCs associated with the 4x4 system, unlike earlier generation trucks. Do you have any pending codes?

 

Thank you!

No codes. It would be better for me to be in 4hi and then be able to take it in. We live way back in the mountains and are pretty much in 4x4 all winter.

Big problem right now is everyone is 3-4 weeks out for work.

 

Are there any pending codes?

How comfortable are you backprobing / testing electrical stuff? Do you have a place to work? Assuming you dont want to work outside in the Alaskan mountains during winter if you can avoid it?

I feel pretty confident we can make this work if you are willing to. Rather than having you stuck in 4Lo until a shop can get you in. @Dm93 might be able to help as well.

 

I’m fairly comfortable testing the electrical stuff. Don’t mind laying in the snow to do so as well.

I didn’t see any pending codes but will run it one more time to be sure.

 

I had this happen to my 2003 gmc 2500hd. The only thing that work was rocking the truck back and forth (manually) while turning the switch from 4w low to 2wd. Took it to a mechanic after that said front locking mechanism was shot. Don't know if its the same issue as you have.

 

I'm unfamiliar with the 3rd gen 4wd system but looking at the wiring diagrams it does appear to operate very similar to the 2nd gen system.
The 3rd gen system is capable of communicating with a scan tool and generating trouble codes, it also has quite a good data list so that would be where I would start.
You would need a scan tool that can communicate with the 4wd ECU which most generic scanners will not.

Here's some info and wiring diagrams.